All electrochemical cells, particularly those equipped with a cation-exchange membrane, suffer from a problem of hardness scale formation on or inside the membrane, as well as on the cathodes. The scale typically consists of hydroxides, carbonates, sulphates and silicates of calcium, magnesium, strontium, iron, manganese, chromium and other heavy metals. It is common practice to acid wash the cell interior to remove the scale during periodic shutdown of the cell and, typically, a 2 to 10% HCl solution is employed for this purpose. To effectively remove scale deposits from inside the membrane, at least one hour, and often longer, acid exposure is required, since both acid penetration and removal of dissolved scale occur by diffusion, an inherently-slow process.
A further disadvantage of the commonly-used acid treatment process is that all cell components made of mild steel, such as the cathode compartment and the cathode itself, undergo severe corrosion during the procedure. When the cathode is in the form of a low mass/high surface area structure, such as expanded mesh or screen, undesired dimensional changes resulting from the corrosion may be significant.